The energy of light is called radiant energy.
There are many different kinds of radiant energy but we can see only a tiny part of the radiant energy that comes from the sun.
This tiny part is called the visible spectrum.
The radiant energy that we cannot see is called the invisible spectrum.
Radiant energy is made up of waves of energy called electromagnetic waves.
Light is one kind of electromagnetic wave.
Radio waves, microwaves, ultraviolet rays, and infrared rays are other kinds of electromagnetic waves.
The waves together form the electromagnetic spectrum.
This is a combination of the visible spectrum and the invisible spectrum.
The sun is the most important natural source of ultraviolet rays.
Most of the ultraviolet rays that are emitted by the sun never reach the earth’s surface at all.
Ultraviolet is very powerful and can be harmful to living things.
If a lot more of the sun’s ultraviolet rays passed through the earth’s atmosphere, plant, animal and human life on earth would be impossible.
Fortunately, there is a layer of a gas called ozone high up in the atmosphere. Ozone prevents most of the ultraviolet rays from reaching us on earth.
We may not be able to see ultraviolet rays, but we can feel their effects.
Too much ultraviolet is bad for us.
In strong sunshine, the skin produces more of a substance called melanin. Melanin protects the skin against sunburn caused by ultraviolet rays.
Fair-skinned people burn more easily than dark-skinned people. Their skin has to produce a large amount of melanin to protect them.
Suntan lotion gives skin extra protection from the sun by absorbing some of the ultraviolet rays.
Ultraviolet rays can be helpful as well as harmful.